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Tuesday, 11 September 2012

Ki-46 Tiger Tail Artifact

Courtesy of Jim Lansdale here is an image of an access cover retrieved from the actual Dokuritsu 18 Hiko Chutai Ki-46 in the heading photograph I posted yesterday. It was recovered by a member of the 1st Air Commando who was at the crash site. The exterior paint which is in pristine condition and is an olive or khaki grey colour close to FS 16350 - or exactly similar to the factory paint found on many early Zero fighters. Jim has reported on the paint colours of another Ki-46 artifact in his collection, part of the tailplane and elevator, at j-aircraft.com hereand I have rendered the colours described in that report as shown below.

5 comments:

So is it possible to assume that fabric covered surfaces of Mitsubishi built IJAAF planes (Ki-15, Ki-21, Ki-30, Ki-46, Ki-67 etc.)would be painted this neutral gray color, and never the gray-green Hairyokushoku as seems to be the case on most of the other IJAAF types?

Could this also be the color of fabric covered surfaces of Mitsubishi built Zero fighters? Could this explain the difference in color hues between metal skin and fabric surfaces of olive gray Zeros (discussed in one of your articles)?

I might be wrong, but I guess similar difference in shades is also visible on some A5M pictures...

One needs to be careful in presuming those are "neutral" greys (pure mixes of black and white pigment). The Munsell values given by Jim for the fabric surfaces are 2.5 Y 6.0/1.0 to 5 Y 6.0/1.0. Although they appear lighter and "greyer" than the metal paint they are still slightly "yellow" or amber tinted greys, probably containing less lamellar anti-corrosive oxide pigments. The metal paint is given as 2.5 Y 4.5/2.5 to 2.5 Y 5.0/2.0 therefore the hue is the same, only the lightness and saturation being different.

Samples of IJAAF Hairyokushoku from the Ki-27, allowing for variance, are approx 1.8 GY 6.7/1.2 to 2.5 GY 7/1. These differ from the Mitsubishi samples only in the degree of "yellow" or amber tint in the grey, being slightly more grey-greenish in appearance. The differences cross the colour spectrum are relatively small, however, and the shifts are easily accounted for by pigment proportion variance and/or age-related ambering. It is perhaps best to think of a "family" of warm greys, some slightly more brownish whilst others are more greenish, both of which tend to oxidise towards more neutral looking, dove or blueish greys.

What about NMF A5Ms? I mean if we assume that Claude's exterior was unpainted metal and not painted aluminum, could it be that ailerons and in certain cases rudder and elevators (though it seems all NMF Claudes had their tail surfaces painted red) were painted gray and not aluminum dope?

The A5M is difficult to be certain about because the presence of the red painted empennage means the examination of fabric surfaces in most photos is limited to the ailerons. Because of deflection the finish on these is not easy to determine. There is no reason to think that silver dope (which can have a rather flat silver-grey finish) was not applied.

The well-known instructions for the Aichi E13A1 suggest that the fabric surfaces could be finished with either silver or grey dope which is presumed to have been to match the overall finish - silver on silver painted aeroplanes and grey on grey painted aeroplanes.

Examination of Zero control surfaces suggests that the fabric dope used by the Japanese was rather advanced for the era, being a pigmented cellulose acetate butyrate which was less flammable and more stable than the more commonly used cellulose nitrate dope. On A6M2 V-110 the fabric surfaces had been finished with a red oxide pigmented dope without apparently any preliminary clear doping then with a grey topcoat finish applied over an earlier grey-green. It is unwise to assume that this type of finish was standard or as factory applied simply because fabric surfaces were subject to continuous maintenance, re-doping, replacement, etc. To quote from the AWM's own treatise on fabric coating:-

"Under normal operational conditions, the fabric surfaces of any aircraft require maintenance. Moisture, ultraviolet light, insects, physical impact and the like all take their toll on the fabric surfaces. For this reason, surfaces require continual patching, repair, repainting and complete recovering at regular intervals. An additional treatment available to the operators of aircraft was a process known as “rejuvenating”. Rejuvenating involves the application of a “dope rejuvenator” to the fabric surface. This softens the dope lacquer, releasing the tension on the fabric. Following the application of rejuvenator an aircraft requires repainting."

The paradox for all nations in the 1940s was that whilst aluminium pigmented dopes and paints were known to be effective in protecting fabric and metal from deterioration and corrosion aluminium was also required in greater quantities for aircraft construction and skinning. This led to the concomitant development in the late 1930s in the UK, Germany, Japan and the USA of various non-aluminium anti-corrosive inorganic pigments in protective paints such as lead chromates, metal oxides, sulfides or sulfoselenides specifically designed to function by an ion-exchange mechanism. These removed ions such as chloride and sulfate which were necessary for the corrosion process to occur. Many of these were of a yellow pigmented character. For the surface protection of aluminium basic zinc potassium chromate (zinc yellow as used in RLM 02), zinc tetroxychromate and strontium chromate (strontium yellow) were used, with the latter being produced in Japan after 1940.

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I first became fascinated by aviation in the Far East at the age of about 7 when my father lifted me into the cockpit of an 'Ohka' rocket-propelled piloted suicide bomb displayed outside the armoury at RAF Cottesmore. It made me think about the people who had designed and built such a weapon . . . and why . . . but especially those who were prepared to fly it - and those who had to face it.